<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>清除内外边距</title>
    <style>
      /* 这个通常是css的第一行代码 */
      * {
        margin: 0; /* 清除外边距 */
        padding: 0; /* 清除内边距 */
      }
      span {
        background-color: pink;
        margin: 20px;
      }
    </style>
  </head>
  <body>
    123
    <ul>
      <li>abcd</li>
    </ul>
    <span>行内元素尽量只设置左右的内外边距</span>
  </body>
</html>
